Crashes on defining a recursive function

[mgold]

Steps to reproduce:

1. Create a custom function
2. Drag the new function into itself

The result is Shadershop becomes unresponsive, and sometimes blanks the thumbnail plots, even on the primitives (top right), showing only the beige background. The symbolic readout says undefined( x ).

This action should be prohibited since it makes no sense mathematically (at least until you can define piecewise functions that allow for a base case).

Also, OH MY FUCKING GAWD THIS IS AMAZING.

[electronicwhisper]

Yeah, it crashes when you drag a function in to itself (or create any kind of circular dependency).

For my own reference, or if anyone wants to tackle it, here is a sketch for a fix:

Write a test that checks when you drag function A into function B that A does not contain B anywhere down the tree and B does not contain A anywhere down the tree.

Patch Actions.addChildFn to make sure that the above is not the case. If it is, don't add the function (and maybe display some sort of warning?).

[mgold]

Thanks for the sketch. This seems to work doesn't account for the case of the added tree containing a compound function, I guess I'll get to that tomorrow:

containsCircularDep = (fn_to_add, existing) ->                                      
  if fn_to_add instanceof C.BuiltInFn                                               
      return false                                                                  
  fn_to_add = fn_to_add.childFns[0].fn                                              
  recurse = (fn) ->                                                                 
    if fn.__id == fn_to_add.__id                                                    
        return true                                                                 
    if fn instanceof C.CompoundFn                                                   
        fn.childFns.some recurse                                                    
    else                                                                            
        false                                                                       
  recurse(existing) 

Then in Actions.addChildFn, right before creating the new childFn,

  if containsCircularDep fn, parent                                              
      console.log "CIRCULAR DEP"                                                 
      return 

What to do once the circular dependency is detected is up to you.

[mgold]

Okay, I've got this version. Let me know if you can break it.

containsCircularDep = (fn_to_add, existing) ->                                      
  if fn_to_add instanceof C.BuiltInFn                                               
      return false                                                                  
  recurse = (fn) ->                                                                 
    if fn instanceof C.DefinedFn or fn instanceof C.CompoundFn                      
        fn == existing or fn.childFns.some recurse                                  
    else if fn instanceof C.ChildFn                                                 
        recurse fn.fn                                                               
    else # C.BuiltInFn                                                              
        false                                                                       
  recurse(fn_to_add) 

The exact semantics are simple once stated: the function being add must not contain its soon-to-be parent anywhere in its tree.

[electronicwhisper]

I like your wording. I pushed some code based on your snippet.

[mgold]

I could have sworn there was a case that required handling C.DefinedFn but I can't break your version. Thanks for merging.

[electronicwhisper]

DefinedFn extends CompoundFn so that case handles it.

[mgold]

Nice!